Glomerularendothelialcellsplaypivotalrolesinthemaintenanceofthenormalstructureandfunction of the healthy glomerulus, and also in the development of glomerular injury in kidney diseases. However, our knowledge of the mechanisms that constantly maintain and regenerate the glomerular endotheliumafterinjuryhavebeenlimited,duetotheinaccessibilityofthiscelltypeandlackofinvivo researchtechnologies.Ourlaboratoryhasrecentlydevelopednoveltransgenicmousemodelsandan intravital imaging approach using serial multiphoton microscopy (MPM) of the same glomerulus over several days-weeks to quantitatively visualize and track the fate and function of the same single glomerularendothelialcellsintheintactlivingkidney.Thistechnicaladvanceprovidedvisualclueson thedevelopmentofclonalendothelialcellclustersattheglomerularvascularpoleinresponsetodietary saltrestrictionandvarioustypesonglomerularinjury,andsuggesteditscontrolbythejuxtaglomerular apparatus (JGA). In addition, the foundation of this proposal is our recent preliminary findings which suggestedthatmaculadensa(MD)cellsoftheJGAarenovelchieforganizersandmasterregulators of glomerular remodeling in the adult kidney. Gene profiling showed that MD cells produce novel secretedtissueremodelingfactorsthatactinaparacrinefashiononresidentprogenitorcells.Oneof thetopnewMDgenesresponsibleforthisnewglomerularremodelingprogramwasidentifiedasCCN1 (alsoknownasCyr61),codingforasecretedangiogenicproteinthatisknowntotargetendothelialcells aswellasothercelltypes.OurmainhypothesisisthatMDcells,viaWntsignaling-mediatedsynthesis andsecretionofangiogenicproteinsincludingCCN1,aremajorparacrineregulatorsoftheglomerular endothelium. This project will use comprehensive experimental approaches including in vitro cell culture, new transgenic mouse models, fluorescently tagged cell lineages, cell fate tracking, in vivo diseasemodelsandserialMPMtoinvestigatetheangiogenicrole,mechanisms,andimportanceofMD cellsandCCN1inglomerularendothelialmaintenanceandrepair.Thespecificaimsareto(i)Examine the role and mechanism of MD cells in the maintenance of normal glomerular capillary structure and function,(ii)StudytheregulationoftheMDcellangiogenesispromotingprogram,and(iii)Testforrenal andcardiovasculardiseasemodifyingrolesandmechanismsofMDcells.